Project Summary Electronic cigarettes (ECs) use heat to aerosolize ?e-liquid? mixtures that usually contain high concentrations of flavor chemicals. This project will purchase 650 commercial e-liquids to: a) identify and quantify the flavor chemicals used plus their degradation reaction products (RxPs) formed upon vaping; and b) evaluate the cellular responses to those flavor chemicals often found at >1 mg/ml (viz. ?dominant flavor chemicals?, DFCs), and to the aerosols produced on vaping. Tested will be 550 ?popular? refill and cartomizer fluids and 100 fluids that have been anecdotally reported to cause sickness in users. Work will be conducted at two campuses: Portland State University for analytical chemistry, and University of California Riverside for human toxicology. Aim 1 (PSU). DFCs and vaping RxPs will be identified and quantified for the 650 fluids. Aerosols made using a range of devices at varied power will be collected in isopropanol and analyzed using gas chromatography/ mass spectrometry (GC/MS) and liquid chromatography/MS/MS. Identification will proceed with standards. RxPs formed from flavor chemicals will be unambiguously distinguished from RxPs from the EC solvents. Aim 2 (UCR). Vape aerosols made using lab-prepared fluids containing the identified DFCs will be made with a range of devices, and screened for cytotoxicity in dose-response experiments using in vitro assays in conjunction with BEAS-2B lung epithelial cells from normal human adults. The aerosols that are most cytotoxic will be studied in depth using an air-liquid interface exposure system with the 3D EpiAirway platform that recapitulates human respiratory epithelium. Individual DFCs will be tested using six cancer-related mode-of- action assays including assays for an epithelial to mesenchymal transition (EMT) that we have observed with some EC products. Alterations in gene expression will be determined using RNA-seq and affected pathways identified. Mixtures of DFCs will be tested at the same relative proportions found in consumer products. Aim 3 (UCR). Since Aim 2 will examine heat generated aerosols, both DFCs and their RxPs products will have been present. Aim 3 will differentiate the DFCs and RxP toxicities by exposing the 3D EpiAirway platform to aerosols generated without heat and containing individual DFCs or the identified RxPs from heating. Endpoint assays will proceed as in Aim 2 to isolate toxicity to individual chemicals. Summary. Little is known about the health effects of flavor chemicals used in ECs. This project will fill an important informational gap with comprehensive new data. Specific toxicants will be identified and the effects of mixing DFCs will be evaluated. Results will be posted on an online database that will be accessible to any interested persons or organization, and will provide foundational information for future understanding of flavor chemicals in tobacco products. The data, the first of their kind, will contribute to a foundation of science upon which the NIH can develop future research directions to protect consumers? health and protect those exposed by second- and thirdhand means.